It is now being determined whether the cases – which are mostly traffic offences but include murder and rape – were affected.

Two men have been arrested over the alleged data manipulation at a Randox Testing Services site in Manchester, and five have been interviewed under caution by police.

Retesting is under way, and so far, there has been no such manipulation on sexual offence, violence or homicide cases.

Gillian Tully, of the Forensic Services Regulator, said all major forensic toxicology suppliers had been asked to carry out a detailed audit of a sample of their cases to ensure the issue was not more widespread.

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The audits uncovered no such data manipulation.

Retesting is under way and set to be completed next year (Picture: Getty)

She said: ‘If there was large-scale manipulation going on across the board I do expect it would have been found during that audit.’

Although no murder and rape cases have yet to be found unreliable, some could be in a lower priority band for testing which have yet to be reanalysed.